1. Field of the Invention
The present invention relates to corrosion inhibition and, more particularly, to inhibiting corrosion of ferrous metals by aqueous brines such as are commonly used in the petroleum industry.
2. Description of the Background
Aqueous brines are commonly used in well servicing fluids, such as drilling fluids, workover fluids, completion fluids, packer fluids, well treating fluids, subterranean formation treating fluids, spacer fluids, hole abandonment fluids, etc. In particular, zinc bromide, calcium bromide and calcium chloride brines and mixtures of these are particularly useful because they are solids free and have high specific gravities.
A relatively severe problem in the use of aqueous brines in well treating applications is the fact that the brines are corrosive to the tubing, casing and other ferrous metal components in and around the well bore. The corrosiveness is especially significant at temperatures above about 250.degree. F., a temperature which is frequently encountered in well bores.
It is known to utilize amines, imidazolines, chromates, phosphates, etc. as corrosion inhibitors in aqueous brines, such inhibitors generally acting to form films on the surface of the ferrous metal components. Likewise, thioureas, thiocyanates, etc. can also be employed to form ferrous sulfide films on the ferrous metal components.
It is also known that certain metals, in conjunction with known corrosion inhibitors, will act to reduce corrosion of ferrous metal in certain media. For example, Russian Patent No. 829884 teaches the incorporation of metallic zinc in a well treating solution which contains hydrochloric acid, the zinc reacting with the HCl to form hydrogen which reduces FeCl.sub.3 to FeCl.sub.2, which in turn does not adversely affect the corrosion inhibitors. U.S. Pat. Nos. 2,635,996; 2,635,997: 2,635,998; 2,635,999 and 2,636,000 to Rohrbach all disclose that metal capsules of metals, such as zinc, magnesium, etc. can aid in providing protection against corrosion in oil and gas wells in the presence of naturally occurring brine. However, the Rohrbach patents are primarily directed to filling the metal capsule with a corrosion inhibiting composition which is released into the well fluid from the capsule.
None of the prior art known to Applicants teaches that particulate metal additives can be used to inhibit corrosion of ferrous metals by aqueous brines of the type used in well servicing operations.